Acrylic acid-based carboxyl group-containing hydrophilic polymers as represented by carboxyvinyl polymers show excellent thickening property with a small amount of use, so that the carboxyl group-containing hydrophilic polymers have been widely used as thickeners in various industrial fields such as cosmetics and toiletries (see, Patent Publication 1). In addition, in the field of cosmetics, in order to further increase a fresh feel of use, a system in which an acrylamide-based thickener and sodium carbonate are used together has been also proposed (see, Patent Publication 2). However, as the amount used increases, there were some disadvantages that the structure is kinked, so that a phenomenon of flaking, so-called kink, is more likely to be caused. In order to solve the occurrence of this kink, a method of adding a high-molecular weight polyethylene glycol as a moisturizing polyhydric alcohol has also been proposed. However, there were some disadvantages that a sticky feel is more likely to be caused, and the transparency during the gelation would be also lowered (see, Patent Publication 3).
In addition, in order to thicken by using the carboxyvinyl polymers, it is necessary to first disperse the carboxyvinyl polymers in water, and thereafter neutralize the dispersion with an alkali such as sodium hydroxide to form a swollen gel. In this dispersing step, it is necessary to neutralize the carboxyvinyl polymer while carefully stirring the dispersion so as not to form a doughy mass, thereby requiring some time. In order to omit this neutralizing step, a thickener that is previously neutralized with an alkali so that a neutralizing step is not needed has been also proposed (see, Patent Publications 4 and 5).